1. Field of the Invention
The present invention relates to a method of bonding bumps of very small metal balls to leads of a TAB tape and an apparatus for arranging bumps used for the same, and in particular to a method of bonding bumps to the tip ends of the leads of a TAB tape for preparing a bump-bonded TAB tape used for TAB (tape Automated Bonding) method which is one of methods of connecting the electrodes of an IC chip with external leads and an apparatus for arranging bumps in a positional relationship corresponding to the lead tip ends of a TAB tape to be bonded.
2. Description of Related Art
A tape Automated bonding (hereinafter referred to as TAB) process is a method of bonding the tip ends of the leads formed in a selected pattern on a TAB tape to the electrodes of an IC chip via metallic bonding projections called as bumps. The bumps are preliminarily mounted either on the leads of the TAB tape or the electrodes of the IC chip and bonding of the TAB tape to the IC chip is performed by heating under pressure by means of a bonding machine. The TAB tape is usually manufactured by forming a film made of a synthetic resin such as polyimide, polyester and the like with sprocket holes or device holes, then laminating a metal foil on the film and thereafter etching the metal foil to form a lead wiring pattern by a photo-resist method.
On the other hand, the bumps through which the TAB tape is connected with the electrodes of semiconductor chips such as ICs and LSIs and the like are often formed on Al electrodes of the semiconductor chips by a plating technique as described in Electronic Part and Materials Vol. 28, No. 7 1989, July, pages 66-76. However, forming bumps on Al electrodes of ICs or LSIs by plating technique costs high and has the possibility of giving damages to the circuits of the semiconductor chip. Therefore, it is not always a preferable process.
One of the methods of forming bumps on the leads of the TAB tape, is disclosed in the Japanese Unexamined Patent Publication No. JP-A-62-28623 and another one, i.e. "a bump transferring method" is described in National Technical Report vol. 31 (1985) No. 3, pages 116-124. The latter method comprises the steps of preliminarily placing bumps on a glass substrate in a predetermined arrangement and transferring the bumps to the leads formed in a selected pattern on a TAB tape.
However, the bump-bonded TAB tapes manufactured by the above methods are not necessarily adequate in view of bonding of the bumps to the electrodes of IC chip, because the bumps are often made in a rectangle-like shape. That is, such TAB tapes involve a problem that the bumps are sometimes bonded to the electrodes of IC chip with variety or less reliability due to the rectangle-like shape, unless the heights of the bumps are accurately equal. Further, since the bumps are formed by plating, there is a restriction such that the material of the bumps must be selected from those alloys or metals which are readily worked by plating.
Spherical bumps are advantageous in view of bonding purpose since they are more deformable than conventional rectangular bumps formed on a glass substrate or the like by plating. However, the spherical bumps involve a problem of how to efficiently arrange the bumps at selected positions and how to readily transfer the bumps to the leads on the TAB tape, since the spherical bumps are manufactured separately before arrangement of the bumps at positions, in contrast to the rectangular bumps which are first formed at selected positions by plating.